Doctor Q said:
Thinking of it another way, % should have two operands. When people omit the second operand, the "default" could be either the number mentioned before it, or it could be the number 1, since (7 % of 1) is (7 / 100).
Given the ambiguity, some calculators handle it one way and others another way.
Yes, or it could mean 9.95 + (0.07 * 20), or 9.95 + (0.07 * arbitrary value) + 20.
Ultimately, % is not strictly an operator. Rather, it is a symbol denoting a concept. Since it is not a mathematical operator, various calculator implementations (hardware and software) implement it as a convenience function but do so in different ways.
I would argue that due to the ambiguity and thus the potential for errors in use, it is far better to ignore this button and handle percentage calculations manually as a multiplication. But then this is also because I believe that people should understand what is going on.
But yes, I think we are agreeing.